Morgagni first described a retroperitoneal tumor in 1761; yet today these lesions remain "obscure" and unrecognized.1-5 The passive attitude of many physicians and surgeons toward retroperitoneal tumors is probably related to their meager experience with these tumors and the supposed rarity of them. The case presented herein is interesting because of the unusual clinical features. This 33-year-old, white man, a bakery worker by occupation, was admitted to the Leech Farm Veterans Administration Hospital on May 20, 1957, having been transferred from the Erie Veterans Administration Hospital. In February, 1957, he began having a "slapping" type of walking, weakness of both legs, more pronounced on the left, and ataxia with a slight tendency to deviate to the left. He was informed by his local physician that the findings were suggestive of a diagnosis of multiple sclerosis. As a result, he was admitted to the Erie Veterans Administration Hospital, where this